1. Technical Field of the Invention
The present invention relates to a core-less rubber crawler having a rubber main body in the shape of an endless belt, wherein a guide protrusion is provided on an internal surface of the rubber main body so as to protrude at a center part of the rubber main body, and a ground contacting lug protrudes on an external surface of the rubber main body.
2. Background Art
A core-less-type rubber crawler is widely used since it has a simple structure and is of low cost. The rubber crawler is structured to be driven by a friction drive between a rubber main body in the shape of an endless belt and a driving wheel or an idle wheel provided on the internal surface of the belt main body.
FIG. 3A is a partial cross-sectional view and a typical example of a conventional core-less-type rubber crawler that will be explained below.
As shown in FIG. 3A, the rubber crawler 11 has a rubber main body 12 extending in a lengthwise direction having a belt shape. A reinforcing cord 15 is embedded in the rubber main body 12 approximately at the intermediate part thereof with respect to the thickness direction. The reinforcing cord 15 is obtained by placing a number of reinforcing filaments side by side and applying a treatment such as gumming thereto. A guide protrusion 13 is provided on the internal surface of the rubber main body 12 in the longitudinal direction along the centerline with respect to the width direction. Furthermore, as shown in of FIG. 3B, the rubber crawler 11 has ground contacting lugs 14A and 14B which protrude from the external surface of the rubber main body, and are alternatively arranged in the left and right side so as to form a zigzag shape.
When the rubber crawler 11 is driven, wheels 17A and 17B such as driving wheels, idle wheels, or tracker wheels roll on the internal surface of the rubber main body 12 at the left and right sides of the guide protrusions 13 provided thereon. In this case, as shown in FIG. 3A, the wheels receive the dispersed load of the vehicle, and the weight of the wheels is perpendicularly applied to the rubber main body 12 on both sides of the guide protrusion 13, in the rubber crawler 11. Thus, the engagement of the wheels with the rubber crawler and the detachment of these are repeatedly performed with generating moment as shown by arrows A. As a result, expansion and contraction in the direction shown by arrows B are continuously repeated in the range of the guide protrusion 13 and a rubber main body 12. Here, a large weight of wheels is applied to the rubber main body 12 at both sides of the guide protrusion 13. Accordingly, the reinforcing cord 15 embedded in the rubber main body 12 is repeatedly subjected to deformation within the rubber main body 12. As a result, it is possible that cracks as shown by arrows C are formed in the vicinity of the basal part of the guide protrusion 13.
FIGS. 4A to 4C are diagrams for briefly explaining a crack generating mechanism at the basal part of the guide protrusion 13 in a conventional rubber crawler. FIG. 4A is a partial cross-section of a conventional rubber crawler.
In FIG. 4A, w represents the load of a wheel, a represents the width of the wheel, and b represents the width of the guide protrusion. The other members or parts are indicated by use of symbols in common with those in FIG. 3A.
FIG. 4B shows a left end of the rubber main body 12 as a reference point x=0, a left basal part of the guide protrusion 12 as a point x=11, a right basal part as a point x=12, and a right end of the rubber main body as a point x=13 in the rubber crawler. Then, the shearing force variation at the points is analyzed.
Concerning load ω per unit length which receives the load of the wheel, a load ω1=(w/2)÷11=w/(2a) when x=0 to 11, and a load ω2=(w/2)÷(13−12)=w/(2a) when x=12 to 13. The load ω in FIG. 4B is shown by numbers of downward arrows on the upper part of a reference plane p–p′ (ground contacting plane).
On the other hand, a repulsive force ω0, which the ground contacting lugs 14A and 14B of a rubber crawler receives based on the load of the wheel, is shown as ω0=w/13=w/(2a+b) when x=0 to 13. The repulsive force ω0 in FIG. 4B is shown by numbers of upward arrows on the lower part of the reference plane p–p′.
The difference between the load ω and the repulsive force ω0 based on the weight of the wheel w produces the shearing force at the parts of x=0 to 13 as shown in FIG. 4C. The shearing force in the range from x=0 to 11 is linearly increased from F10=0 to F11=(ω0−ω1)×a, and the shearing force in the range of 11 to 12 is F(11+12)=0 since only the repulsive force from the ground surface affects in this range. Then, it can be seen that the shearing force in the range of from x=12 to 13 linearly decreases from F12=(ω0−ω1)×a−ω0b to F13=0.
It is therefore the object of the present invention to provide a rubber crawler for solving the above-mentioned conventional problem, and which effectively prevents the crack from generating by the shearing force restriction at the basal part of the guide protrusion.